The improvement of RF sample probes is crucial to the development of high field biological solid state NMR. Unlike solution NMR, solid state NMR techniques require exposing the delicate biological sample to very high intensity radio frequency (RF) magnetic fields. Unless the electric field component E of these fields is minimized, the sample will very likely be heated to destruction before the experiment is completed. In Core B, we will apply the "low-E" technology that we have developed for double frequency widebore NMR to the important areas of triple resonance and more accessible standard bore magnets. We will also adapt these probes for the sample/flow applications that are a centerpiece of the proposal. The technology developed in this Core will not only be needed to carry out the scientific program described in the proposal, but it will broadly impact the ability of NMR spectroscopists to conduct protein structure and dynamics studies in the solid state. Any area of health and medicine that benefits from a better understanding of proteins may be affected.